PDMK is a barrier to gases and in particular to oxygen and furthermore possesses barrier properties to moisture. It is of use in the manufacture of monolayer structures or of multilayer structures comprising a layer of PDMK and at least one layer of another material. These structures are of use in the manufacture in particular of food packagings which have to be sterilized or pasteurized.
U.S. Pat. No. 5,169,994 discloses a process for the manufacture of 2,2,4,4-tetramethylcyclobutane-1,3-diol comprising the stages consisting:
(1) in introducing IBAN into a pyrolysis region, in which the IBAN is heated to a temperature of 350 to 600° C., in order to produce an exiting vapor stream comprising DMK, IBA and unreacted IBAN;
(2) in rapidly cooling the exiting vapor stream, in order to condense the IBA and the IBAN and to separate the condensate from the DMK vapor;
(3) in introducing the DMK vapor into an absorption region, in which the DMK vapor is brought into contact with and dissolved in a solvent comprising an ester comprising from 4 to 40 carbon atoms and composed of the reaction product of an aliphatic carboxylic acid and of an alcohol, in order to produce an exiting stream comprising a solution of DMK in the solvent;
(4) in introducing the exiting stream from the absorption region into a dimerization region, in which the effluent is heated to a temperature of 70 to 140° C., in order to convert the DMK to 2,2,4,4-tetramethylcyclobutane-1,3-dione, in order to produce an exiting stream comprising a solution of 2,2,4,4-tetramethylcyclobutane-1,3-dione in the solvent; and
(5) in introducing the exiting stream from the dimerization region into a hydrogenation region, in which the exiting stream is brought into contact with a hydrogenation catalyst under hydrogenation pressure and temperature conditions, in order to produce an exiting stream comprising a solution of 2,2,4,4-tetramethylcyclobutane-1,3-diol in the solvent.
In the description, it is specified that the pyrolysis stage is fed with IBAN generally as a mixture with an inert gas and under a reduced pressure, such as 20 to 500 torr. It is not known whether the reduced pressure relates to the IBAN, because of the presence of inert gas, or whether it is the mixture of IBAN and of inert gas which is under reduced pressure. In example 1, the pyrolysis of the IBAN is carried out at 250 torr and the gas recovered, after separation of the IBA and IBAN, is composed of 97% of DMK. Thus, there was no diluting gas. The degree of conversion of the IBAN in the pyrolysis, that is to say the ratio of the amount of IBAN pyrolyzed to the amount of IBAN entering the pyrolysis region, is 60%.
U.S. Pat. No. 5,258,256 discloses a process which is very similar to the preceding process but the conditions for the pyrolysis of the IBAN, with regard to the presence of inert gas, are no clearer. It is only shown in the examples that the pressure of the pyrolysis is 87, 105 or 123 torr.